1. Technical Field
The present invention relates generally to cast fabrications and more particularly to a cast fabrication having a cast portion and an insert of a material dissimilar to that of the cast portion.
2. Discussion
The design criteria for many types of housings typically includes considerations for the strength as well as the overall weight of the housing. This is particularly true for housings designed for use in highway vehicles, such as automobiles and trucks. One such component employed by such vehicles is a differential housing which supports the axles and drive shaft of a vehicle. Conventionally, differential housings have been formed out of lightweight materials, such as aluminum, to reconcile the competing design criteria of strength and weight.
While this strategy has provided satisfactory results with the engine and drive train combinations known in the art, the modern trend of vehicle manufacturers is toward vehicles having more power and torque. In some instances, conventional differential housings have not been satisfactorily integrated into such new vehicles with sufficient durability and failures have been noted in high-stress areas, primarily in the area where the drive shaft is supported for rotation within the differential housing. Attempts to improve the durability of the prior art differential housings have included various measures ranging from the fabrication of the differential housing from different materials having improved load carrying characteristics to the complete redesign of the axle system. Neither solution, however, has proven to be entirely satisfactory.
The use of a different material, such as cast iron, for example, entails not only a substantial weight penalty, but also substantial increases in the fabrication piece costs due to increased variability in the casting processes where the aluminum differential housing had been die cast. Additionally, conversion to a different material may necessitate the purchase of new equipment designed specifically to machine the new material. Examples of such equipment could range from new spindles, feed screws and tool resharpening equipment, to new machine tools designed to accommodate the specific characteristics of the material to be machined. In addition to being extremely costly, this approach may not be implementable in a given facility due to floor space limitations where production of conventional differential housings is still required.
The second alternative, redesigning the complete axle system, is also extremely costly, typically requiring vast resources to design, model and test the new axle system. Furthermore, the final design of many components is based on criteria established by "concurrent engineering" groups which utilize input from several disciplines, such as those associated with the casting, machining, assembly and servicing of the axle system. This additional criteria permits the component to be fabricated and serviced in a reliable and cost-effective manner. While such "concurrent engineering" efforts generally produce high quality, robust components, it is frequently difficult and costly to accommodate even the key fabrication and servicing concerns where the component is subjected to loads generating high stresses.